Mud volcanoes and gas hydrates in the Black Sea: new data from Dvurechenskii and Odessa mud volcanoes

Bohrmann, Gerhard; Ivanov, M.K.; Foucher, Jean-Paul; Spieß, V.; Bialas, J.; Greinert, Jens; Weinrebe, Wilhelm; Abegg, Friedrich; Aloisi, Giovanni; Artemov, Yu. G.; Blinova, V.; Drews, Manuela; Heidersdorf, F.; Krabbenhöft, Anne; Klaucke, Ingo; Krastel, Sebastian; Leder, Tea Duplančić; Polikarpov, Igor; Saburova, Maria; Schmale, Oliver; Seifert, Richard; Volkonskaya, A.; Zillmer, Matthias

doi:10.1007/s00367-003-0157-7

Cited by 122 publications

(88 citation statements)

References 26 publications

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“…The methane concentrations reported here are affected by degassing during and after core retrieval due to loss of hydrostatic pressure (e.g., Dickens et al, 1997;Paull et al, 2000) and therefore represent minimum values. Site 214 lies within the methane hydrate stability field, located below $720 m water depth in the Black Sea (Bohrmann et al, 2003;Naudts et al, 2006;Pape et al, 2010). Remarkable degassing features in the sediment, probably due to gas hydrate destabilization induced by pressure release, were observed in this core at about 260 cmbsf.…”

Section: Pore Water Analysesmentioning

confidence: 99%

Diagenetic barium cycling in Black Sea sediments – A case study for anoxic marine environments

Henkel¹,

Mogollón²,

Nöthen³

et al. 2012

Geochimica et Cosmochimica Acta

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High-resolution sedimentary records of major and minor elements (Al, Ba, Ca, Sr, Ti), total organic carbon (TOC), and profiles of pore water constituents (SO 2À 4 , CH 4 , Ca 2+ , Ba 2+ , Mg 2+ , alkalinity) were obtained for two gravity cores (core 755, 501 m water depth and core 214, 1686 m water depth) from the northwestern Black Sea. The records were examined in order to gain insight into the cycling of Ba in anoxic marine sediments characterized by a shallow sulfate-methane transition (SMT) as well as the applicability of barite as a primary productivity proxy in such a setting. The Ba records are strongly overprinted by diagenetic barite (BaSO 4 ) precipitation and remobilization; authigenic Ba enrichments were found at both sites at and slightly above the current SMT. Transport reaction modeling was applied to simulate the migration of the SMT during the changing geochemical conditions after the Holocene seawater intrusion into the Black Sea. Based on this, sediment intervals affected by diagenetic Ba redistribution were identified. Results reveal that the intense overprint of Ba and Ba xs (Ba excess above detrital average) strongly limits its correlation to primary productivity. These findings have implications for other modern and ancient anoxic basins, such as sections covering the Oceanic Anoxic Events which Ba is frequently used as a primary productivity indicator. Our study also demonstrates the limitations concerning the use of Ba xs as a tracer for downward migrations of the SMT: due to high sedimentation rates at the investigated sites, diagenetic barite fronts are buried below the SMT within a relatively short period. Thus, 'relict' barite fronts would only be preserved for a few thousands of years, if at all.

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Section: Pore Water Analysesmentioning

confidence: 99%

Diagenetic barium cycling in Black Sea sediments – A case study for anoxic marine environments

Henkel¹,

Mogollón²,

Nöthen³

et al. 2012

Geochimica et Cosmochimica Acta

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“…In the northwestern Black Sea, there are numerous shallow seeps (depths, 35 to 800 m), which emit methane. Also, off the shelf (Ͼ1,500 m), deep active seeps have been detected (8,17,38). These seeps contribute massive but unknown amounts of methane to the Black Sea water column.…”

mentioning

confidence: 98%

Evidence of Intense Archaeal and Bacterial Methanotrophic Activity in the Black Sea Water Column

Durisch-Kaiser

Klauser

Wehrli

et al. 2005

Appl Environ Microbiol

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In the northwestern Black Sea, methane oxidation rates reveal that above shallow and deep gas seeps methane is removed from the water column as efficiently as it is at sites located off seeps. Hence, seeps should not have a significant impact on the estimated annual flux of ϳ4.1 ؋ 10 9 mol methane to the atmosphere [W. S. Reeburgh, B. B. Ward, S. C. Wahlen, K. A. Sandbeck, K. A. Kilatrick, and L. J. Kerkhof, Deep-Sea Res. 38(Suppl. 2):S1189-S1210, 1991]. Both the stable carbon isotopic composition of dissolved methane and the microbial community structure analyzed by fluorescent in situ hybridization provide strong evidence that microbially mediated methane oxidation occurs. At the shelf, strong isotope fractionation was observed above high-intensity seeps. This effect was attributed to bacterial type I and II methanotrophs, which on average accounted for 2.5% of the DAPI (4,6-diamidino-2-phenylindole)-stained cells in the whole oxic water column. At deep sites, in the oxic-anoxic transition zone, strong isotopic fractionation of methane overlapped with an increased abundance of Archaea and Bacteria, indicating that these organisms are involved in the oxidation of methane. In underlying anoxic water, we successfully identified the archaeal methanotrophs ANME-1 and ANME-2, each of which accounted for 3 to 4% of the total cell counts. ANME-1 and ANME-2 appear as single cells in anoxic water, compared to the sediment, where they may form cell aggregates with sulfate-reducing bacteria

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“…In many ways the Gulf of Mexico has also served as a case study for understanding gas hydrate deposits and hydrocarbon seeps, which have more recently been investigated on other continental margins. Gas hydrates have similarly been reported from active oil seeps in the South China Sea [Chen et al, 2006;Huang et al, 2006], the west coast of Africa [Ben-Avraham et al, 2002;Gay et al, 2006;Sahling et al, 2008], and the Black Sea [Bohrmann et al, 2003]. We argue that conditions or rapid, focused flux of oil and gas that prevail at hydrocarbon seeps will necessarily produce shallow deposits of gas hydrate that are metastable under prevailing oceanographic conditions.…”

Section: Background and Geologic Settingmentioning

confidence: 96%

“…One facet of this issue is how active gas seepage through the seafloor causes gas hydrate to form not in zones buried under 100s of meters of sediment, but at the sediment water interface. This phenomenon was first observed in piston cores collected for surface geochemical exploration in the Gulf of Mexico [Brooks et al, 1984] and has subsequently been observed in diverse global settings including the Black Sea [Bohrmann et al, 2003], the Congo margin , and the Pakistan margin [Delisle, 2004]. In this type of setting, gas hydrate is subject to much more variable temperature conditions than it is emplaced in BSR deposits [I. R. MacDonald et al, 1994] and preliminary evidence suggested that in the upper slope depths (~500m), where many of the Gulf of Mexico hydrates have been documented, brief excursions in bottom water temperature could induce decomposition of shallow gas hydrate deposits.…”

Section: Stability and Occurrence Of Gas Hydrate At Seepsmentioning

confidence: 99%

Remote Sensing and Sea-Truth Measurements of Methane Flux to the Atmosphere (HYFLUX project)

MacDonald¹

2011

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A multi-disciplinary investigation of distribution and magnitude of methane fluxes from seafloor gas hydrate deposits in the Gulf of Mexico was conducted based on results obtained from satellite synthetic aperture radar (SAR) remote sensing and from sampling conducted during a research expedition to three sites where gas hydrate occurs (MC118, GC600, and GC185). Samples of sediments, water, and air were collected from the ship and from an ROV submersible using sediments cores, niskin bottles attached to the ROV and to a rosette, and an automated sea-air interface collector.The SAR images were used to quantify the magnitude and distribution of natural oil and gas seeps that produced perennial oil slicks on the ocean surface. A total of 176 SAR images were processed using a texture classifying neural network algorithm, which segmented the ocean surface into oil-free and oilcovered water. Geostatistical analysis indicates that there are a total of 1081 seep formations distributed over the entire Gulf of Mexico basin. Oil-covered water comprised an average of 780.0 sq. km (sd 86.03) distributed with an area of 147,370 sq. km. Persistent oil and gas seeps were also detected with SAR sampling on other ocean margins located in the Black Sea, western coast of Africa, and offshore Pakistan.Analysis of sediment cores from all three sites show profiles of sulfate, sulfide, calcium and alkalinity that indicated anaerobic oxidation of methane with precipitation of authigenic carbonates. Difference among the three sampling sites may reflect the relative magnitude of methane flux.Methane concentrations in water column samples collected by ROV and rosette deployments from MC118 ranged from ~33,000 nM at the seafloor to ~12 nM in the mixed layer with isolated peaks up to ~13,670 nM coincident with the top of the gas hydrate stability field. Average plume methane, ethane, and propane concentrations in the mixed layer are 7, 630, and 9,540 times saturation, respectively. Based on the contemporaneous wind speeds at this site, contemporary estimates of the diffusive fluxes from the mixed layer to the atmosphere for methane, ethane, and propane are 26.5, 2.10, and 2.78 µmol/m 2 d, respectively.Continuous measurements of air and sea surface concentrations of methane were made to obtain high spatial and temporal resolution of the diffusive net sea-to-air fluxes. The atmospheric methane fluctuated between 1.70 ppm and 2.40 ppm during the entire cruise except for high concentrations (up to 4.01 ppm) sampled during the end of the occupation of GC600 and the transit between GC600 and GC185. Results from interpolations within the survey areas show the daily methane fluxes to the atmosphere at the three sites range from 0.744 to 300 mol d-1.Considering that the majority of seeps in the GOM are deep (>500 m), elevated CH 4 concentrations in near-surface waters resulting from bubble-mediated CH 4 transport in the water column are expected to be widespread in the Gulf of Mexico. HYFLUX Final Report iiTexas A&M University -Corpus Christi...

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Mud volcanoes and gas hydrates in the Black Sea: new data from Dvurechenskii and Odessa mud volcanoes

Cited by 122 publications

References 26 publications

Diagenetic barium cycling in Black Sea sediments – A case study for anoxic marine environments

Diagenetic barium cycling in Black Sea sediments – A case study for anoxic marine environments

Evidence of Intense Archaeal and Bacterial Methanotrophic Activity in the Black Sea Water Column

Remote Sensing and Sea-Truth Measurements of Methane Flux to the Atmosphere (HYFLUX project)

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